A. Field of Invention
This invention pertains to an internal combustion for a motor vehicle with recycled exhaust gas, and more particularly to a method and apparatus for recycling exhaust gas which is automatically adjusted for variations in the atmospheric pressure due to elevational changes.
B. Description of the Prior Art
In conventional internal combustion engines with exhaust gas recycling systems, an exhaust gas recycling valve is provided which is controlled as a function of the rotational speed of the engine and its load. More particularly this valve is closed when the engine is starting, idling or operating at full load, and is partially opened when the engine is under a partial load to control the exhaust gas recycling rate. However if the motor vehicle is operated at higher elevations, the exhaust gas recycling rate is reduced since the intake manifold pressure is unchanged while the exhaust gas counter pressure is reduced with increased elevation resulting a smaller differential pressure at the valve. This reduced exhaust gas recycling rate results in a lower conversion by the catalytic converter and makes it more difficult to recognize misfires. Moreover, normally the exhaust gas recycling system is monitored by a temperature sensor in the exhaust return line and since this sensor indicates a slight increase in temperature at lower exhaust gas recycling rates, the exhaust gas recycling monitoring system becomes unreliable.
In German Patent No. 30 30 128 a sensor for atmospheric pressure is provided to correct the exhaust gas recycling rate for changes in the elevation. This sensor interrupts recycling of the exhaust gas when the atmospheric pressure drops. However this arrangement does not solve the above-mentioned problems but rather amplifies them. In addition this arrangement is expensive since it requires an additional sensor and pipelines for its connection to the gas exhaust recycling system.
In German Patent Offenlegungsschrift No. 37 29 468 an apparatus for recycling exhaust gas is shown with an electromagnetic valve. German patent No. 34 28 380 shows a similar system with a special electronic valve coupled to atmospheric pressure.